Head protection helmets conventionally use polymer foam liners to attenuate impacts and distribute impact forces over larger areas. Helmet liners may use a rigid polymer, a compressible foamed polymer, or a combination of rigid and compressible. Prior art helmet liner systems are normally designed to be durable enough to endure repeated impacts. Helmet shells are thin hard plastic to guard against puncture, cutting or scratching injuries while the foam liners spread the force of impact from the point of impact to a larger area but are not designed to dissipate appreciable amounts of impact energy.
The example of the invention described herein uses a single sacrificial gas or liquid fluid-filled bladder installed in the occipital foam liner. Bladders can be used in any number of impact locations and in practice there would ideally be between two to six bladders for any liner. However for simplicity and ease of understanding, only one bladder is shown in the example described herein. Multiple bladders could be situated in the interior shell of a helmet, with the size, location and distribution of the bladders based on expected or typical impact locations.
In the example herein an occipital foam liner of a prior art liner system was modified to include a single sacrificial gas or liquid fluid-filled bladder to dissipate impact energy by releasing the fluid when a severe impact is encountered. Below the threshold pressure, the bladder serves as a fluid-filled cushion within the foam liner. When an impact force attains a pre-selected impact maximum force, a fluid release control valve opens rapidly and fluid is released at a controlled flow rate through a flow restricting orifice preferably. The pressurized fluid, such as a liquid or gas vents to the atmosphere through the flow restricting orifice which dissipates a significant portion of the impact energy. The reduction in impact decelerations was measured to be 68% (P<0.0001) compared to a helmet using a standard rigid foam and compressible foam liner. When impact forces were below the selected threshold for activation of the fluid release control valve, there was a reduction in impact decelerations of approximately 23%, although this difference is not considered statistically significant due to the small number of tests used in the experiment.
Helmets are used to prevent or minimize head injury of the wearer. Expected impacts include both sharp impact, for which a helmet is intended to prevent cuts and penetration of the striking object into the head and skull, and blunt impacts, in which the head is rapidly decelerated or accelerated which can cause a concussion.
Many helmets consist of a hard polymer shell to protect against sharp impacts, with interior elastic or foam polymer padding to minimize the risk of concussive impacts.
The use of the Head Injury Criterion (HIC) parameter has been found to be an effective measure of the risk of concussive injury. HIC has been found to be linearly dependent on the acceleration or deceleration of the wearer's head at the time of impact. If the acceleration or deceleration of the head and brain within the skull is severe enough, a concussive injury could result. Conversely, decreasing the degree of acceleration or deceleration of the head and brain at the time of impact reduces the risk of concussive injury.
The conventional use of elastic or foam polymer compressible and rigid padding for the lining of a helmet tends to dissipate the forces from blunt impacts by spreading the distribution of force over a larger area and by compressing to a degree. The conventional liner of a helmet also effectively secures the helmet to the head of the wearer and prevents dislodging of the helmet on impact so that it remains in place to protect the wearer. If the helmet's foam liner is too hard, it will be uncomfortable for the wearer, and will transfer impact forces more directly to the head and brain. If the helmet liner is too soft, the helmet and liner will move around during use. To retain a soft lined helmet in place the wearer will tend to adjust the chin strap and size of the shell to make the helmet tighter, which compresses the soft padding until the compliance is reduced to be similar to that of a harder liner padding.
Accordingly for the reason explained above, some designs for helmet liner padding use an elastic polymer. The use of an elastic polymer helmet liner allows for the distance over which the head and brain decelerates upon an impact to be increased compared to a harder non-elastic helmet liner padding. The compression of the elastic polymer generally decreases the deceleration forces experienced by the head and brain, and reduces the risk of a concussive injury compared to hard foam liners.
However, if the interior helmet padding has significant elastic recovery properties, such as when expanded polypropylene (EPP) or expanded polyethylene (EPE) are used, the head and helmet rebound or reverse direction rapidly on impact. The rebound effect can increase the total accelerations experienced by the brain. Therefore elimination of rebound is desirable. Rebound of the head and brain during impact using an elastic helmet liner padding can increase the risk of a concussive injury.
Features that distinguish the present invention from the background art will be apparent from review of the disclosure, drawings and description of the invention presented below.